This invention relates in general to computer-based electronic instruments and more particularly to a method and apparatus for controlling and coordinating the operation of several such instruments.
In recent years microcomputer-based electronic equipment has been developed for performing various test, control, computation and other functions according to stored instruction sets. The use of microprocessors in, for instance, test instruments allows instrument settings to be changed during tests without human intervention, thereby accelerating test procedures in which instrument settings must be changed many times. Microcomputer-based test instruments also typically provide for storage of acquired test data in random access memories, for manipulation and display after a test is complete, thereby freeing operators from the task of monitoring data displays during the test and writing down test results.
Many electronic equipment tests, computations, control functions or the like involve the use of more than one instrument and difficulties often arise in coordinating their operation. For instance, a digital-to-analog converter (DAC) is often tested by applying a known digital quantity as an input to the DAC, sampling and digitizing the DAC output, and then comparing the digitized output with the input. The process is typically repeated for many different input quantities to test the DAC over its fully input range. The use of a microcomputer-based pattern generator to produce sequences of inputs and a computer-based digitizer to sample and store the resulting sequence of outputs can speed up the testing process since the operator need not change the pattern generator output or write down the digitizer output after each test. However, to test the speed of the DAC, the digitizer must sample the output of the converter at a selected time after the converter input has changed. Therefore the operation of the pattern generator and the digitizer must be synchronized. In the past, the pattern generator has been adapted to produce a trigger signal when it has changed its output pattern, and that trigger signal was applied to the digitizer through an appropriately adjusted time delaying device to initiate sampling. The digitizer is adapted to produce another trigger signal when it has completed sampling and digitizing of the converter output. That trigger signal is applied to the pattern generator to initiate generation of the next output pattern.
This traditional approach to coordinating test instrument operation requires instruments to be interconnected by temporary wiring, employing timers, counters and other logic devices in a fashion dictated by the requirements of the particular test to be performed. Such temporary interfacing of equipment is often difficult and time-consuming to install, unsightly and unreliable. What is needed is an apparatus permitting precise time coordination of the operation of many different computer-based test instruments or other equipment in the performance of a wide variety of test, control, computation or other functions without requiring installation of custom interconnect equipment and wiring to coordinate instrument operation.
Some procedures requiring more than one instrument involve the transfer of data between instruments. For instance, one computer-based test instrument may repeatedly acquire and pass test data to another instrument which uses it in some fashion to control a real-time function which must be synchronized with the operation of the first instrument. In order to perform in this way, it is necessary not only that the operation of the separate instruments be synchronized, but also the data must be transferred rapidly so as to avoid impeding the real-time operation of the instruments. It would be useful to have an apparatus which would not only synchronize the operation of separate instruments but would provide high-speed data transfer between such instruments.